During operations in which general anesthesia is used, it is common to administer anesthetic gases through a flexible endotracheal tube which passes through the mouth and into the trachea of the patient. In order to obtain positive control over the patient's breathing and the administration of the anesthesia, it is necessary to block a portion of the trachea exterior to the endotracheal tube. Such blockage should completely seal off passage of air between the distal and proximal ends of the trachea, exterior to the endotracheal tube. This is typically accomplished by using an inflatable cuff hermetically sealed to the tube in proximity to the tube's distal end. The cuff, when inflated, conforms intimately to the wall of the trachea, thus sealing the tracheal passage exterior to the tube.
Because of the relaxed state of the patient, it is necessary to monitor the patient's heart while the patient is under the influence of anesthesia. Monitoring of the heart may consist of simply listening to the heart rate, including electronically monitoring the heart rate with respect to minimum and maximum values. It is preferable, however, to monitor the heart in such a way that the actual sounds made by the various components of the heart may be heard clearly and distinctly. Information pertaining to the state of a patient's condition can be discerned from these sounds by a skilled anesthesiologist. Such information would be used to determine subsequent administration of anesthetic, or to advise the surgeon of the condition of the patient.
In some cases, monitoring is accomplished by external means such as an EKG monitor. Such external means do not provide a proper reproduction of heart sound, however, and therefore are generally unacceptable. Moreover, since EKGs are electromechanical devices, there is a substantial time delay between the onset of a particular heart condition and the recording of such condition by the machine.
It is possible to monitor heart sounds using a sound monitoring means located in the esophagus. An esophageal monitoring means, however, may produce a signal that can be quite noisy due to variations in body fluids in the esophagus during surgery. Another problem is the introduction of a second tube into the mouth, in addition to the endotracheal tube, thus creating undesirable crowding and trauma.
It has been found that endotrachial monitoring of the heart produces the most useful and consistent results. It is possible to hear various characteristic sounds of the heart, and to distinguish them from other extraneous sounds such as breathing. All known forms of endotrachial monitoring devices are pneumatic in nature, and interface with an electro-acoustic sensing device external to the patient's body, through a lumen in the endotracheal tube. This allows breathing sounds to be transmitted via the lumen.
In addition to being able to monitor the heart, it is sometimes required that the heart be artificially stimulated into beating in a rhythmic manner. This artificial electrical stimulation, known as pacing, may be either atrial or ventricular. It has been found, however, that ventricular pacing is used with variable success. Atrial pacing, which has been developed more recently, is generally more successful. Two types of atrial pacing are typically used: direct and esophageal. Direct atrial pacing involves placement of electrodes on the left atrium during open heart surgery. Esophageal atrial pacing involves introduction of a lead into the esophagus such that a pair of electrodes contacts the wall of the esophagus closest to the heart. A series of current pulses is subsequently delivered through these electrodes, thus stimulating the left atrium.
The invention shows some characteristics in common with the prior art shown in U.S. Pat. Nos. 4,263,921 to Trugillo, 4,331,156 to Apple et al., 4,383,534 to Peters, and Canadian patent No. 1,209,213 to Teves.
In Apple et al., an esophageal cardiac pulse probe is disclosed wherein a flexible diaphragm contacts the inner wall of the esophagus. Pressure variations in the diaphragm due to movement in the esophagus are transmitted through a lumen to an external electrical transducer. The lumen is concentric with a larger second lumen, which is used for direct acoustic monitoring.
Peters discloses a device that operates on a principle similar to Apple, but is inserted into the trachea, not the esophagus. Also disclosed are a lumen that is an integral part of the endotracheal tube wall and an EKG sensing device mounted on the exterior of the endotracheal tube at the distal end. Exterior mounting of any device is not desirable since the device could become dislodged from the apparatus. Peters teaches that it is desirable to monitor cardiac sounds from the trachea as opposed to the esophagus due to its proximity to the heart. Moreover, Peters is concerned with monitoring breath sounds together with cardiac monitoring.
Teves distinguishes from Peters by teaching an endotracheal device for monitoring heart sounds only, with different structure that attentuates respiratory sounds reaching the lumen by placing the lumen external to the endotracheal tube. Additionally, Teves discloses an inflatable cuff that is longer and more pliant that other cuffs, which reduces irritation of the trachea inner wall.
Trugillo discloses an endotracheal tube and inflatable cuff apparatus that has a temperature sensing means embedded in the wall of the tube adjacent to the proximal end of the cuff. This configuration solves the possible problem of dislodging inherent in Peters. The wires associated with the temperature sensing device are located in a lumen in the wall of the tube. However, Trugillo does not address the problem of endotracheal monitoring using any kind of sensor means within the cuff.